Thesis (M.Sc.)--Chulalongkorn University, 2013

Thenus unimaculatus or a purple-legged shovel-nosed lobster is one of three Thenus species found in Thailand which can only be found along the coast line of the Andaman Sea. Shovel-nosed lobsters Thenus have been increasingly consumed and this could give a great threat to T. unimaculatus which has a narrow range of distribution. Genetic diversity study of the purple-legged shovel-nosed lobster is therefore needed for evaluating its current genetic status. In this study, 83 T. unimaculatus specimens were collected from five provinces in Thailand along the Andaman Sea. 12s ribosomal RNA gene (12S rDNA) and cytochrome C oxidase subunit I (COI) gene in mitochondrial DNA were amplified and sequenced. The 12S rDNA and COI nucleotide sequence alignments were successfully prepared and revealed that their haplotype diversity and nucleotide diversity were 96.12% and 0.54%, respectively. Results from phylogenetic analysis, AMOVA, and Fst values suggested that the populations of T. unimaculatus in Thailand were fairly mixed. This homogeniety of T. unimaculatus populations could indicate a seasonal circulation of its planktonic larvae in the Andaman Sea, resulting from different patterns of sea surface currents between the north-eastern and the south-western monsoon seasons. Moreover, the high haplotype diversity and low nucleotide diversity values, the negative values of neutrality test, and the unimodal pattern of mismatch distribution infer that the T. unimaculatus population have recently undergone a population expansion after bottle neck event which probably caused by the change of sea level during the end of last glacial maximum period. The only threat directly to the species would be an over-exploitation and continuous genetic structure study of T. unimaculatus is still necessary for planning a better exploitation and conservation strategy.